Certain known types of such apparatuses operate on the principle of mixing the gas charged with solid particles with scrubbing water in the form of a spray whose fineness may be varied, so that the solid or semi-solid particles are collected by the droplets of scrubbing water. The scrubbed gas is then exhausted on one side, while the scrubbing water and the collected solid particles are recovered on another side.
A known type of such apparatus includes water-spraying devices situated in or in the vicinity of the flow of gas to be scrubbed, and combined with throat devices such as perforated plates or the like. Mixing of the gas with the scrubbing water is generated by the speed of the gas passing through the throat device. At the periphery of the flow, this speed causes induction of the scrubbing water which is entrained in the downstream flow. Such apparatus generally includes a plurality of scrubbing stages in series so that the head loss of the flow of gas per stage remains acceptable for good mixing. Each stage includes a throat device, e.g. of the perforated plate type, and at least one set of scrubbing water sprayers. The particles collected from the flow of at least partially scrubbed gas are separated from the scrubbing water by inertia. Such an apparatus also includes a closed circuit device for recycling and re-using the scrubbing water. The charged scrubbing water is therefore conveyed from stage to stage towards a settling tank or the like, where it is recycled prior to being sent back to the spray devices.
To ensure that the apparatus is properly effective, the water must be distributed properly by the sprayers, and this means that spray nozzles having small cross-sectional areas must be used. Unfortunately, the recycled scrubbing water is never entirely free of particles, or even large-volume agglomerations of particles that did not settle out during recycling. These impurities are entrained back to the spray devices with the recycled scrubbing water, and they form deposits on the inside of the spray devices, or they even partially or totally block the spray nozzles. Naturally, this reduces the effectiveness of the apparatus.
After the particles have been collected, they form agglomerations which constitute most of the residue obtained by the apparatus. If such agglomerations are not removed as they are formed, they increase in volume, and, when the apparatus is stopped, they are deposited and become stuck inside the scrubbing chambers of each stage. Naturally, the complexity of the return circuit for the scrubbing water charged with agglomerations is increased by the presence of multiple scrubbing stages.